The role and extent of dextral transpression and lateral escape on the post-Acadian tectonic evolution of south-central New England
The role and extent of dextral transpression and lateral escape on the post-Acadian tectonic evolution of south-central New England
复制标题
右旋压扭和侧向逃逸对新英格兰中南部后阿卡迪亚构造演化的作用和程度
DOI：
10.2475/01.2017.02
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发表时间：
2017
影响因子：
2.9
通讯作者：
L. Rohrer
中科院分区：
文献类型：
--
作者：
M. Massey;D. Moecher;T. B. Walker;T. O'Brien;L. Rohrer
基岩填图、构造分析、运动学和相关岩石组构的记录以及详细的锆石和独居石年代学是对新英格兰南部阿卡迪期后构造演化的新解释的基础。缅因州中部和布朗森山带东半部的早期组构以平面面理、近水平线理和右旋运动学指标为特征。随着扭压作用的发展，构造和组构反映了缩短作用的增加，表现为面理变紧，近等斜褶皱发育，反向高应变带局部化，陡峭的倾角平行线理，以及自顶向东的反向运动学指示。同构造矿物组合表明，冷却伴随变形，与垂直挤压成分一致。相反，从康涅狄格州到新罕布什尔州，布朗森山带的西半部具有自顶向南的左行变形特征，包括两个区域左行剪切带，构成了西布朗森山剪切系统。新的锆石和独居石年代学以及以前发表的结果表明，从∼350 Ma到∼295 Ma，右行扭压持续进行。在∼360 Ma至∼355 Ma闪长岩、英云闪长岩和花岗岩岩浆作用之后，开始了右旋挤压作用。在Bronson山东部和缅因州中部，由∼330 Ma发育的硅线石级别反向高应变带，而较低级别组构、变质锆石边缘的存在和已公布的角闪石冷却年龄表明，变形至少持续到∼295 Ma。西布朗逊山剪切系的左旋自顶向南变形先于∼330 Ma至∼300 Ma的十字石变质作用，同构造独居岩和大量已发表的资料表明变形一直持续到∼285 Ma。共轭剪切带在空间和时间上是相连的，表明新英格兰地区基岩出露中的主要组构、构造和矿物组合是由石炭纪递进的右旋挤压和侧向逃逸驱动的，比以往的任何构造重建都要年轻得多。这个模型可以解释新英格兰的一系列神秘特征，包括对比运动学、岩性和岩石构造带的差异折返以及佩勒姆穹顶。这些特征归因于始于密西西比纪的劳伦斯边缘和阿瓦隆/梅古马之间的斜向会聚，而不是人们长期以来提出的早-中泥盆世阿卡迪亚造山作用。纽约海角和魁北克海湾之间的位置可能提供了必要的几何形状，以集中新英格兰的变形和侧向逃逸，并将该地区的造山带缩短近一个数量级。
Bedrock mapping, structural analysis, documentation of kinematics and associated petrofabrics, and detailed zircon and monazite geochronology are the basis for a new interpretation of the post-Acadian tectonic evolution of southern New England. Early fabrics in the Central Maine Zone and eastern half of the Bronson Hill Zone are characterized by planar foliations, subhorizontal lineations, and dextral kinematic indicators. As transpression progressed, structures and fabrics reflected an increased component of shortening, marked by tightening of foliations, development of closed to isoclinal folds, localization of reverse high strain zones, steep dip-parallel lineations, and reverse top-to-east kinematic indicators. Syntectonic mineral assemblages show that cooling attended deformation, consistent with a component of vertical extrusion. In contrast, the western half of the Bronson Hill Zone is characterized by sinistral top-to-south deformation from Connecticut to New Hampshire, including two regional sinistral shear zones, and comprise the Western Bronson Hill Shear System. New zircon and monazite geochronology, along with previously published results, show that dextral transpression progressed continuously from ∼350 Ma to ∼295 Ma. Dextral transpression was initiated following ∼360 Ma to ∼355 Ma dioritic, tonalitic, and granitic magmatism. Sillimanite-grade reverse high strain zones developed by ∼330 Ma, while the presence of lower-grade fabrics, metamorphic zircon rims, and published hornblende cooling ages show deformation continued to at least ∼295 Ma in the eastern Bronson Hill and Central Maine. Sinistral top-to-south deformation in the Western Bronson Hill Shear System preceded ∼330 Ma to ∼300 Ma staurolite grade metamorphism, and syntectonic monazite and an abundance of published data show that deformation continued to ∼285 Ma. The conjugate shear zones were spatially and temporally linked, indicating that the dominant fabrics, structures, and mineral assemblages in bedrock exposures in this area of New England were driven by progressive dextral transpression and lateral escape in the Carboniferous, much younger than any previous tectonic reconstruction. This model can explain an assortment of enigmatic features in New England, including contrasting kinematics, differential exhumation of lithologies and lithotectonic zones, and the Pelham dome. These features are attributed to oblique convergence between Laurentian margin and Avalon/Meguma beginning in the Mississippian, rather than the Early to Middle Devonian Acadian orogeny as has long been proposed. The location between the New York promontory and the Quebec embayment could have provided the necessary geometry to focus deformation and lateral escape in New England, and shorten the orogen in this area by almost an order of magnitude.